1. New Results on the EMC Effect at Large x in Light to Heavy Nuclei
Patricia Solvignon
Argonne National Laboratory
For the E Collaboration
Good afternoon.
I am going to present today new results from Jlab experiment E on the EMC effects in light to heavy nuclei with an emphasis at large x.
The spokepeople of this experiment are John Arrington and Dave Gaskell and the graduate students are Aji Daniel and Jason Seely who graduated last year.
spokespersons: J. Arrington and D. Gaskell
graduate students: A. Daniel and J. Seely
Hall C Summer Workshop
August 9-10, 2007

2. Nuclear structure functions and the EMC effect
Nuclear structure: A  Z.p + N.n
Effects found in several experiments at CERN, SLAC, DESY
Same x-dependence in all nuclei
Shadowing: x<0.1
Anti-shadowing: 0.1<x<0.3
EMC effect: x>0.3
The size of the effect
is a function of A
In early 80’s, it was discovered that in the nuclear structure, the cross section is not simply the sum over its constituents protons and neutrons.
This discovery was called the “EMC effect” from the name of the collaboration that first made the observation.
Morever, the quark distribution in nuclei has a strong x-dependence which is the same for all nuclei with the shadowing region at x<0.1, the anti-shadowing region for x between 0.1 and 0.3 and the EMC effect region at x>0.3.
It was also found that the size of the effect depends on the atomic number A.
E139 (Fe) EMC (Cu) BCDMS (Fe)

3. Mapping the EMC Effect Models should include conventional effects:
Fermi motion and binding dominate at high x
Binding also affects quark distribution at all x
Then more “exotic” explanations may be added if these effects are not enough to describe the data like:
Nuclear pions
Multiquark clusters
Dynamical rescaling
Theoretical activities have since then tried to map out the EMC effect.
It seems that most the ideas converge on common requirements which are that models should include fermi motion and binding because these effects dominate at high x. Binding effects also extend to all x.
Then, if the Fermi motion-binding contribution are not enough to reproduce the data, more exotic explanations can be added like nuclear pions, multiquark clusters, dynamical rescaling.
(read blue sentence)
For exemple, here a plot from Benhar et al comparing their calculation to SLAC and EMC data. It can be seen that the model including nuclear pions does reproduce well the data in the for x between 0.2 and 0.75.
Many of these models can reproduce the large x region but failed in other x-regions or for other data (Drell-Yan) or didn’t include conventional effects.
Benhar, Pandharipande, and Sick
Phys. Lett. B410, 79 (1997)

4. EMC effect in few-body nuclei
Calculations predict different x-dependence for 3He and 4He
Different models predict different x-dependence
Some models predict different shapes for 3He and 4He
Spectral functions are easier to calculate for light nuclei
Data lower quality
Lower precision for 4He
No data at large x for 3He
For few-body nuclei, the models disagree on the x-dependence and the shape of the EMC effect.
The world data for light nuclei have a low precision or are missing in the large x as for 3He.

5. Existing EMC Data
SLAC E139 most extensive and precise data set for x>0.2
A/D for A=4 to 197
4He, 9Be, 12C, 27Al, 40Ca,
56Fe, 108Ag, and 197Au
Size at fixed x varies with
A, but shape is nearly constant
E will improve with
Higher precision data for 4He
Addition of 3He data
Precision data at large x and
on heavy nuclei
 Lowering Q2 to reach high x region

6. Quark-hadron duality
I. Niculescu et al., PRL85:1182 (2000)
First observed by Bloom and Gilman in the 1970’s on F2:
Scaling curve seen at high Q2 is an accurate average over the resonance region at lower Q2
To access the large x region, one needs a Q2 of above 18GeV2.
But the phenomenom of quark-hadron duality may be of great help to access this region by lowering our W2 cut on the data to be included.

7. Quark-hadron duality
J. Arrington, et al., PRC73: (2006)
First observed by Bloom and Gilman in the 1970’s on F2:
Scaling curve seen at high Q2 is an accurate average over the resonance region at lower Q2
To access the large x region, one needs a Q2 of above 18GeV2.
But the phenomenom of quark-hadron duality may be of great help to access this region by lowering our W2 cut on the data to be included.
In nuclei, the averaging is in part done by the Fermi motion.

8. EMC effect: Scaling at lower Q2, W2
JLab E89-008:
Q2 ~ 4 GeV2
1.3<W2<2.8 GeV2
data in the resonance
region
E data at higher Q2, with precise measurement of Q2-measurement
J. Arrington, et al., PRC73: (2006)

9. JLab Experiment E03-103
Ran in Hall C at Jlab Summer and Fall 2004 (w/E  x>1)
A(e,e’) at 5.77 GeV
Targets:
H, 2H, 3He, 4He,
Be, C, Al, Cu, Au
10 angles to measure
Q2-dependence
All targets at large angles: 40, 46 and 50.
C and D data at all angles to verify precise scaling and our extraction of the EMC ratio is Q2-dependence.

10. JLab Experiment E03-103
Ran in Hall C at Jlab Summer and Fall 2004 (w/E  x>1)
A(e,e’) at 5.77 GeV
Targets:
H, 2H, 3He, 4He,
Be, C, Al, Cu, Au
10 angles to measure
Q2-dependence
All targets at large angles: 40, 46 and 50.
C and D data at all angles to verify precise scaling and our extraction of the EMC ratio is Q2-dependence.
E coverage

11. E03-103: Experimental details
Main improvement over SLAC due to improved 4He targets:
Source of uncertainty
Statistics
*Density fluctuations
Absolute density
SLAC E139 %
1.4%
2.1%
JLab E03-103 %
0.4%
1.0%
(1.5% for 3He)
* - size of correction is 8% at 4 uA vs % at 80 uA
SLAC: high power pulsed beam, gas target?
JLAB: much higher density: (cryo not gas target), raster, heat compensation system

12. E03-103: Experimental details
Main improvement over SLAC due to improved 4He targets:
Source of uncertainty
Statistics
*Density fluctuations
Absolute density
SLAC E139 %
1.4%
2.1%
JLab E03-103 %
0.4%
1.0%
(1.5% for 3He)
* - size of correction is 8% at 4 uA vs % at 80 uA
Main drawback is lower beam energy:
Requires larger scattering angle to reach same Q2
Larger - contamination
Large charge-symmetric background
Larger Coulomb distortion corrections
Ratio of e+ to e- production
Ratio of e+ to e- production
Say something about e+/e-: worse case and we can compare with ratio at lower angle

13. E03-103: Analysis status Analysis is in the final stage
Cut off at x=2
Analysis is in the final stage
Cross section extraction
Calibrations, efficiency corrections, background subtraction completed
Finalizing model-dependence in radiative corrections, bin centering, etc…
Investigating Coulomb distortion corrections (heavy nuclei)
EMC Ratios: Isoscalar EMC correction (requires n/p)
Investigating the rules of n/p ratio at large x (x> )

14. E03-103: Carbon EMC ratio and Q2-dependence
Preliminary

15. E03-103: Carbon EMC ratio and Q2-dependence
Preliminary

16. E03-103: Carbon EMC ratio and Q2-dependence
Preliminary

17. E03-103:Comparison of Carbon and 4He
Nuclear dependence of cross sections
Preliminary

18. E03-103: Preliminary 3He EMC ratio
Large correction for proton excess
Preliminary

19. E03-103: Preliminary 3He EMC ratio
Large correction for proton excess
Preliminary
Significant EMC effect
Different shape at large x than for the heavier nuclei
Calculations underestimate the effect

20. Coulomb distortions on heavy nuclei
Initial (scattered) electrons are accelerated (decelerated) in Coulomb field of nucleus with Z protons
Not accounted for in typical radiative corrections
Usually, not a large effect at high energy machines – not true at JLab (6 GeV!)
E uses modified Effective
Momentum Approximation (EMA)
Aste and Trautmann,
Eur, Phys. J. A26, (2005)

21. E03-103: EMC effect in heavy nuclei
E data corrected for coulomb distortion
Scale errors: 1.2-2%
Preliminary

22. E03-103: EMC effect in heavy nuclei
E data corrected for coulomb distortion
Preliminary observation:
Large and low x cross-overs A-independent
Preliminary

23. EMC effect in heavy nuclei
Corrected for coulomb distortion
E data corrected for coulomb distortion
Preliminary observation:
Large and low x cross-overs A-independent
Good agreement with the SLAC data for Fe
Preliminary

24. EMC effect in heavy nuclei
Corrected for coulomb distortion
E data corrected for coulomb distortion
Preliminary observation:
Large and low x cross-overs A-independent
Good agreement with the SLAC data for Fe and Au
About 1% correction for coulomb distortions in SLAC data
Preliminary

25. A or (A) dependence of the EMC effect ?
Good agreement between E and SLAC E139 data after Coulomb corrections.
Preliminary E results confirm A and density dependence of the EMC effect.
x = 0.6
E data with CC
SLAC data with CC
Density dependence is tricky: we don’t really know how to calculate it, especially for 3He.
Adding heavy nuclei data doesn’t bring much, but the light nuclei constrain a lot more fits.
Preliminary

26. A or (A) dependence of the EMC effect ?
Good agreement between E and SLAC E139 data after Coulomb corrections.
Preliminary E results confirm A and density dependence of the EMC effect.
x = 0.6
E data with CC
SLAC data (no CC)
Preliminary

27. Summary JLab E03-103 provides:
Precision nuclear structure ratios for light nuclei
Access to large x EMC region for 3He  197Au
Preliminary observations:
Scaling of the structure function ratios for W<2GeV down to low Q2
Carbon and 4He have the same EMC effect
Large EMC effect in 3He
Similar large x shape of the structure function ratios for A>3
More to come:
Absolute cross sections for 1H, 2H, 3He and 4He: test models of n/p and nuclear effects in few-body nuclei
Quantitative studies of the Q2-dependence in structure functions and their ratios

28. Extra slides

29. Isoscalar Corrections
SLAC param. (1-0.8x)
CTEQ
NMC fit
Isoscalar correction applied to data Au
3He

30. Scaling of the nuclear structure functions
F2(x,Q2) consistent with QCD evolution in Q2 for low x values (x<0.5)
Huge scaling violations at large x (especially for x>1)
F2(,Q2) consistent with QCD evolution in Q2 to much larger  values
Scaling violations are mostly the “target-mass” corrections (plus a clear contribution from the QE peak)
 Nearly independent of A

31. E03-103: Charge-symmetry background
Ratio of e+ to e- production
=40o

32. E03-103: Charge-symmetry background
Ratio of e+ to e- production
=40o
=50o

33. Scaling of the nuclear structure functions
Low Q2 JLab data (from E89-008, 4 GeV) are consistent with extrapolated structure function from high Q2 SLAC data [ fixed dln(F2)/dln(Q2) ]
Above =0.65, there is a large gap between JLab, SLAC data, but there are indications of scaling up to =0.75

34. Scaling of the nuclear structure functions
Low Q2 JLab data (from E89-008, 4 GeV) are consistent with extrapolated structure function from high Q2 SLAC data [ fixed dln(F2)/dln(Q2) ]
Above =0.65, there is a large gap between JLab, SLAC data, but there are indications of scaling up to =0.75
Our data fill in the gap up to ~0.75, show indications of scaling up to ~0.9